Lithium secondary battery containing organic electrolyte, active material for cathode thereof, and method for manufacturing the active material

ABSTRACT

The lithium secondary battery uses lithium or a compound containing lithium as an anode active material, and lithium nickel oxide as a cathode active material. This battery is produced to enhance the charge and discharge capacity. The lithium nickel oxide is prepared as follows. Nickel oxide which contains nickel of more than trivalence or a nickel salt which produces nickel of more than trivalence when heated, and lithium salt are mixed at an Li/Ni (molar salt ratio) of 1.0 to 1.5. After preheating the mixture, it is baked at a temperature of 680° C. to 780° C. in an oxygen atmosphere, thus producing a lithium nickel oxide. The primary differential absorption spectrum of the electron spin resonance of the lithium nickel oxide is a singlet (single line) when measured by use of an X band at a temperature of 77 K., and the line distance (ΔHpp) between the peaks is 140 mT or more. The intensity ratio of the main peak of the components other than the lithium nickel oxide and that of the lithium nickel oxide in a powder X-ray diffraction image is lower than 0.03. The Li/Ni ratio (atomic ratio) is above 0.9, and the grain size of the primary particles is below 1 μm.

The present invention relates to a lithium secondary battery,particularly relates to a lithium secondary battery comprising a lithiumnickel oxide as an improved cathode active material, the cathode activematerial and a method for preparing the same.

BACKGROUND OF THE INVENTION

The lithium nickel oxide is LiNiO₂ when the ratio of Li (lithium) and Ni(nickel) is 1:1 (atomic ratio) exactly according to the stoichiometriccomposition ratio, and possesses a lamellar structure same as LiCoO₂ orthe like, and hence its utility as cathode active material for lithiumsecondary battery is expected.

However, in the conventional synthesis of lithium nickel oxide, theratio of Li and Ni tends to be deviated from the stoichiometriccomposition ratio, and Ni invades into the Li layer and the lamellarstructure is disturbed, and therefore when used as a cathode activematerial for a lithium secondary battery, the charging and dischargingcapacity is smaller than the value expected from LiNiO₂ with Li and Niatomic ratio of 1:1.

Specifically describing the method of synthesis of conventional lithiumnickel oxide and the Li/Ni atomic ratio of thus synthesized lithiumnickel oxide, hitherto, the lithium nickel oxide was synthesized byheating the lithium hydroxide hydrate (LiOH.H₂ O) and nickel (Ni) powderin oxygen (O₂) atmosphere at 750° C. for 12 hours, pulverizing again,and further baking, as disclosed, for example, in Japanese PatentTokkosho No. 63-59507.

What is actually obtained is, however, not LiNiO₂ at the stoichiometriccomposition ratio of 1:1 (atomic ratio) of Li and Ni, but instead acomposition of Li₀.85 Ni₁.15 O₂, having a Li/Ni ratio (atomic ratio) is0.74, in which the lamellar structure was disturbed, and when used ascathode active material for lithium secondary battery, only a battery ofsmall charging and discharging capacity was obtained as mentioned above.

If Li/Ni ratio (atomic ratio) is 1 according to the stoichiometriccomposition ratio, since it is possible that the crystal configurationof Li and Ni is random or disorder and it is believed that a part of Nimay invade into the layer of Li, thereby charging and dischargingcapacity being decreasing.

It is hence the first object of the present invention to provide alithium secondary battery having a large charging and dischargingcapacity by solving the problem of small charging and dischargingcapacity of the lithium secondary battery when the lithium nickel oxidesynthesized in the conventional method is used as cathode activematerial.

It is also the second object of the present invention to provide acathode active material used in said lithium secondary battery.

Moreover, it is the third object of the present invention to provide amethod for manufacturing the cathode active material used in saidlithium secondary battery.

DISCLOSURE

The invention is achieved by synthesizing the lithium nickel oxide to beused as cathode active material for lithium secondary battery, bymixing 1) a nickel oxide containing nickel with valence of 3 or more ora nickel salt for producing nickel with valence of 3 or more by heating,and 2) a lithium salt, at Li/Ni (molar salt ratio)=1.0 to 1.5, andheating, thereby synthesizing a lithium nickel oxide of which primarydifferential absorption spectrum of electron spin resonance measured ata temperature of 77 K. by using X band is a singlet, and intensity ratioof main peak other than lithium nickel oxide and peak of lithium nickeloxide in powder X-ray diffraction image (CuKα ray) is 0.03 or less.

That is, the present invention is to provide a lithium secondary batterycontaining organic electrolyte using lithium or a compound containinglithium as an anode, lithium nickel oxide as the active material for acathode and organic electrolyte, wherein the cathode active material isa lithium nickel oxide of which primary differential absorption spectrumof electron spin resonance measured at temperature 77 K. by using X bandis a singlet, and intensity ratio of main peak other than the lithiumnickel oxide and main peak of the lithium nickel oxide in powder X-raydiffraction image (CuKα ray) is 0.03 or less.

Furthermore, the present inventors have found that the lithium nickeloxide having the said characteristics concerning to the spectrum ofelectron spin resonance and the intensity ratio of the peaks in powderX-ray diffraction image, and the electronic structure which indicatesthe line width (ΔHpp) between the peaks of the primary differentialabsorption spectrum of the electron spin resonance is 140 mT or more, issuperior as a cathode active material and can provide a lithiumsecondary battery having a large charging and discharging capacity.

That the primary differential absorption spectrum of electron spinresonance of lithium nickel oxide is a singlet even at a lowertemperature means that the nickel (Ni) in the lithium nickel oxide has avalence of 3 and that the electron state around nickel is suited tocharging and discharging function, which fact has been found for thefirst time by the inventors. That is, hitherto, there have been reporteda correlation between the X-ray diffraction and the charging anddischarging capacity and a correlation between the nickel valency andthe charging and discharging capacity, but they have not alwayscoincided with the charging and discharging capacity.

The present inventors investigated into the synthesis of lithium nickeloxide by using nickel oxide (Ni₂ O₃) and synthesized one large incharging and discharging capacity. Analyzing it by electron spinresonance, we have found that such lithium nickel oxides of highcapacity present a certain signal in electron spin resonance. Thus, inthe lithium nickel oxide of which primary differential absorptionspectrum of electron spin resonance is singlet, the Li/Ni ratio (atomicratio) is almost always 1, which make it possible to provide the lithiumsecondary battery with large charging and discharging capacity.

The electron spin resonance spectrum is measured at temperature 77 K.because exchange of magnetic energy into thermal motion energy oflattice vibration is decreased by lowering the measuring temperature soas to intensify the absorption strength and it is possible to measure ata relatively low cost because 77 K. is the boiling point of liquidnitrogen. It is, however, possible to measure in a range of 50 K. to 120K.

In the powder X-ray diffraction image of the lithium nickel oxide, theintensity ratio of 0.03 or less of the main peak of other than lithiumnickel oxide and the main peak (appearing at 2θ=18° to 19°) of lithiumnickel oxide means that the content other than lithium nickel oxide, orimpurity is very small, and thus the lithium nickel oxide is high inpurity and small in impurity, thereby a lithium secondary battery oflarge charging and discharging capacity may be obtained.

The present inventors also found that, as the lithium nickel oxide usedfor a cathode active material of the said lithium secondary battery, thelithium nickel oxide containing nickel with valence of 3 or more ornickel salt for producing nickel with valence of 3 or more by heating,and lithium salt, are mixed to be close to 1 at Li/Ni (atomic ratio) andmake the average grain size of the primary particles below 1 μm. Thematerial is preferred to make the charging and discharging capacitylarge. Accordingly, the present invention is to provide the lithiumsecondary battery containing organic electrolyte, wherein Li/Ni ratio(atomic ratio) of the lithium nickel oxide is 0.9 or more and theaverage grain size of the primary particles is 1 μm or less.

Examples of nickel oxides containing nickel with valence of 3 or more ornickel salts producing nickel with valence of 3 or more by heatinginclude nickel oxide (III) (Ni₂ O₃), NiOOH, Li₂ NiO₃, and Li₂ NiO_(3-a)wherein 0<a≦0.3. Among them, nickel oxide (III) (Ni₂ O₃) is particularlypreferable because lithium nickel oxide of high capacity is obtained.

Nickel oxide (III) is not obtained in a pure form of Ni₂ O₃, but H₂ O orOH group is likely to be contained slightly. That is, Nickel oxide (III)is not obtained in a complete unhydrate form, always in a hydrate form.The inventors determined the Ni content per unit weight of nickel oxideby titration, and 0.698 g to 0.710 g of Ni was contained in 1 g ofsample, which nearly coincides with the calculated value in Ni₂ O₃ (Nicontent of 0.7098 g), and hence it was identified to be a nickel saltwith valence of 3. According to the thermal analysis to measure theweight variation while raising the temperature, it is observed thatoxygen is discharged from the oxide and the weight loss is coincidedwith the weight difference between Ni₂ O₃ and NiO, and hence it was alsoidentified to be the nickel salt with valence of 3.

As examples of lithium salt, lithium oxide (Li₂ O) and lithium hydroxidehydrate (LiOH.H₂ O) are available. In particular, lithium hydroxidehydrate (LiOH.H₂ O) is preferable as its Li source to synthesize lithiumnickel oxide because the melting point is low and it is easily mixeduniformly.

In the invention, in synthesis of the lithium nickel oxide, the nickeloxide containing nickel with valence of 3 or more or the nickel saltproducing nickel with valence of 3 or more by heating is used as its Nisource because it is easy to produce lithium nickel oxide containingnickel with valence of 3, and it is also easy to obtain a lithium nickeloxide of which atomic ratio of Li and Ni ((1-x)/(1+x)) in Li_(1-x)Ni_(1+x) O₂ is close to the stoichiometric composition ratio of 1:1(atomic ratio) by preventing the entry of nickel with valence of 2.

In synthesis of lithium nickel oxide, 1) a nickel oxide containingnickel with valence of 3 or more or nickel salt producing nickel withvalence of 3 or more by heating, and 2) a lithium salt are mixed, andthe mixture is heated. This heat treatment should be done in an oxygenstream, under an oxygen pressure, or in an oxygen atmosphere, because itis suited to obtain lithium nickel oxide closer to the stoichiometrycomposition ratio.

That is, when heated in oxygen atmosphere, the stability of nickel withvalence of 3 is increased, and formation of nickel with valence of 2 canbe inhibited, so that it is easier to produce an ideal lithium nickeloxide with the Li/Ni ratio (atomic ratio) close to 1.

Therefore, the present invention is to provide a method for synthesizingthe lithium nickel oxide used for a cathode active material for thelithium secondary battery, which comprises steps of mixing 1) a nickeloxide of more than trivalence or a nickel salt which produces nickel ofmore than trivalence when heated and 2) a lithium salt at an Li/Ni(molar salt ratio) of 1.0 to 1.5, baking the mixture at a temperature of680° C. to 780° C. after preheating, preferably in an oxygen atmospheresuch as in the oxygen stream or under the oxygen pressure.

Moreover, in synthesis of lithium nickel oxide, the mixing ratio of 1)the nickel oxide containing nickel with valence of 3 or more or thenickel salt producing nickel with valence of 3 or more by heating and 2)lithium salt is preferred in a range of Li/Ni ratio (molar salt ratio)of 1.0 to a slightly lithium salt excessive Li/Ni ratio (molar saltratio) of 1.5. In particular, the Li/Ni ratio (molar salt ratio) ispreferred to be in a range of 1.01 to 1.3, more preferably Li/Ni ratio(molar salt ratio) of around 1.1.

Thus, in the heat treatment, the Li/Ni ratio (molar salt ratio) ispreferred to be slightly larger than 1 because lithium salt is likely tobe evaporated in the heat treatment and the Li/Ni ratio (molar saltratio) tends to be lower in the synthesized lithium nickel oxide, and itis also preferred to mix at the Li/Ni ratio (molar salt ratio) of 1.5 orless because, if the Li/Ni ratio (molar salt ratio) is more than 1.5,the unreacted lithium salt impedes the charging and discharging reactionin the battery system, resulting in a smaller charging and dischargingcapacity. The Li/Ni ratio (atomic ratio) in the synthesized lithiumnickel oxide can be determined by measuring the Li content by the atomicabsorption method, and measuring the Ni content by the chelate titrationmethod.

The Li/Ni ratio (atomic ratio) of lithium nickel oxide is preferred to0.9 or more, because the lamellar structure is not disordered and it iseasy to obtain the lithium secondary battery of large discharge anddischarge capacity. The Li/Ni ratio (atomic ratio) of lithium nickeloxide is preferred to be closer and closer to 1 of the stoichiometriccomposition ratio, but it may exceed 1 and be reached to about 1.5.

In the present invention, the average grain size of lithium nickel oxideis preferred to be 1 μm or less, because if it exceed 1 μm, the reactingsurface area is decreased as a cathode active material and the chargeand discharge capacity becomes small. There is no problem in thedischarge performance even if the smaller grain is used. However, it isnot easy to handle the smaller ones, therefore the average grain size of0.3 μm or more is preferred to use. The grain size of lithium nickeloxide in the present invention is determined by SEM (Scanning ElectronMicroscope) and such grain size is sometimes different from thatdetermined by particle size distributor such as laser diffractionsystem.

The temperature of heat treatment at synthesizing lithium nickel oxideis preferred in a range of 680° to 780° C., because, when thetemperature of heat treatment is less than 680° C., the reactionprogress is slow, and when the temperature of heat treatment exceeds780° C., the Li/Ni atomic ratio in lithium nickel oxide becomes smallerand the particle size larger. The heat treatment time is preferred in arange of 5 to 30 hours, though variable depending on the temperature ofheat treatment.

In the above heat treatment, before raising to 680° to 780° C., it ispreferred to heat preliminarily to 400° to 600° C. This is becausenickel with valence of 3 is unstable against heat, and if heated to 680°to 780° C. at once, it is likely to be transformed into nickel withvalence of 2. The duration of this preliminary heating is notparticularly limited, but usually it is preferred to be about 1 to 10hours.

Therefore, the heat treatment should be done through a step ofpreliminary heating, and it is particularly preferred to preheat to 400°to 600° C. for 2 to 4 hours, and then heat to 680° to 780° C. for 5 to20 hours, and the latter step of heat treatment may be called "baking"to be distinguished from preheating. It is preferred to carry out theheat treatment, of course, in an oxygen atmosphere such as oxygen streamand oxygen pressure.

In the invention, the lithium nickel oxide refers to the compoundexpressed as LiNiO₂ when Li and Ni are synthesized in the stoichiometriccomposition ratio of 1:1 (atomic ratio), but actually the ratio of Liand Ni is often deviated from the stoichiometric composition ratio, andtherefore it is mentioned as "lithium nickel oxide", not "LiNiO₂ " inthe specification.

The cathode is prepared by mixing the lithium oxide with, as required,electron conduction aids such as phosphorous graphite and acetyleneblack, and binders such as polytetrafluoroethylene and polyvinylidenefluoride, and forming the obtained cathode mixture by proper means.

The anode is composed of lithium or a lithium containing compound, andthis lithium containing compound is classified into a lithium alloy andothers.

Examples of lithium alloy include lithium-aluminum, lithium-lead,lithium-indium, lithium-gallium, and lithium-indium-gallium. Examples oflithium containing compound other than lithium alloy include a carbonmaterial with lamellar structure, graphite, tungsten oxide, and lithiumiron complex oxide.

Among these examples of lithium containing compound, some do not containlithium at the time of manufacture, but when acting as the anode, theyare transformed in a state containing lithium. Above all, graphite ispreferred from the viewpoint of large capacity density.

The electrolyte is an organic electrolyte prepared by dissolving one ortwo or more electrolytes selected from the group consisting of LiCF₃SO₃, LiC₄ F₉ SO₃, LiClO₄, LiPF₆, and LiBF₄ in a single solvent or amixed solvent of two or more types selected from the group consisting of1,2-dimethoxy ethane, 1,2-diethoxy ethane, propylene carbonate, ethylenecarbonate, γ-butyrolactone, tetrahydrofuran, 1,3-dioxylane, diethylcarbonate, dimethyl carbonate, and methyl ethyl carbonate. Among them,propylene carbonate, ethylene carbonate, and methyl ethyl carbonate areparticularly preferred because they are excellent in the cyclecharacteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of lithium secondarybattery according to the present invention.

FIG. 2 is a diagram schematically showing electron spin resonancespectrum of lithium nickel oxide used as cathode active material inExamples 1 to 4 and Comparative Example 2.

FIG. 3 is a diagram schematically showing electron spin resonancespectrum of lithium nickel oxide used as cathode active material inComparative Example 1.

FIG. 4 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 1.

FIG. 5 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 2.

FIG. 6 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 3.

FIG. 7 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 4.

FIG. 8 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in ComparativeExample 1.

FIG. 9 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in ComparativeExample 2.

FIG. 10 is a diagram schematically showing electron spin resonancespectrum of lithium nickel oxide used as cathode active material inExamples 5 to 7 and Comparative Example 5.

FIG. 11 is a diagram schematically showing electron spin resonancespectrum of lithium nickel oxide used as cathode active material inComparative Example 3.

FIG. 12 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 5.

FIG. 13 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 6.

FIG. 14 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in Example 7.

FIG. 15 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in ComparativeExample 3.

FIG. 16 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in ComparativeExample 4.

FIG. 17 is a diagram schematically showing X-ray diffraction image oflithium nickel oxide used as cathode active material in ComparativeExample 5.

DETAILED DESCRIPTION OF THE PREFERRED EXAMPLES

The invention is further described below specifically by referring toembodiments. The invention is, however, not limited to these embodimentsalone.

EXAMPLE 1

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were heated, and lithium nickel oxide was synthesized. This synthesiswas conducted in the following procedure.

Lithium hydroxide hydrate and nickel oxide (III) were weighed to be aratio of Li/Ni=1.1/1 (molar salt ratio), and pulverized and mixed byusing a ball mill. The mixture was preheated to 500° C. in oxygen streamfor 2 hours, and raised up to 700° C. at heating rate of 50° C./hr orless, and baking at 700° C. was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured at temperature 77 K. by using X band, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 2, and the line width (ΔHpp) between peaks was 166 mT.

To measure the electron spin resonance of lithium nickel oxide, electronspin resonance measuring instrument ESP300E made by BRUCKER Inc. wasused, and a powder sample was put in a quartz capillary and sealed invacuum, and it was inserted into a liquid nitrogen Dewar vessel, andusing X-band, it was measured at 77 K., the boiling point of liquidnitrogen.

The line width (ΔHpp) between peaks of the primary differentialabsorption spectrum was determined by correcting the line width obtainedfrom FIG. 2 by using Mg²⁺ /MgO standard sample. The powder X-raydiffraction image of synthesized lithium nickel oxide is schematicallyshown in FIG. 4. The intensity ratio of main peak other than the lithiumnickel oxide and main peak of the lithium nickel oxide obtained fromthis powder X-ray diffraction image was 0.0098.

That is, the main peak of the lithium nickel oxide was a peak appearingat 2θ=18° to 19°, and its intensity was 99067 cps (counts per sec), andthe main peak of other than the lithium nickel oxide was a peakappearing at 2θ=31.68°, and its intensity was 972 cps, and the intensityratio of the main peak of other than the lithium nickel oxide and themain peak of the lithium nickel oxide was 0.0098 as mentioned above.

Incidentally, the intensity ratio of the main peak of other than thelithium nickel oxide and the main peak of the lithium nickel oxide isobtained in the following formula, supposing the ratio to be R, theintensity of main peak of other than lithium nickel oxide to be P₁, andthe intensity of main peak of lithium nickel oxide to be P₀.

    R=P.sub.1 /P.sub.0

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.93. This Li/Ni ratio (atomic ratio) in the synthesized lithiumnickel oxide can be determined by measuring the Li content by the atomicabsorption method, and measuring the Ni content by the chelate titrationmethod. The average grain size of the primary particles of thesynthesized lithium nickel oxide was 0.5 μm.

By using the lithium nickel oxide thus synthesized by heating as cathodepositive material, and mixing it with phosphorous graphite as electronconduction aid and polytetrafluoroethylene as binder at a rate of80:15:5 (ratio by weight), a cathode mixture was prepared.

Pouring the cathode mixture into a mold, it was pressed and formed in adisk of 10 mm in diameter at 1 t/cm², and heated at 250° C. and acathode was obtained Using this cathode, a button type lithium secondarybattery in the structure as shown in FIG. 1 was fabricated.

In FIG. 1, reference numeral 1 is the cathode, 2 is an anode made of adisk-shaped lithium of 14 mm in diameter. 3 is a separator made of fineporous polypropylene film, and 4 is an electrolyte absorber made ofnonwoven polypropylene cloth. 5 is a stainless steel cathode can, 6 is astainless steel mesh cathode current collector, and 7 is a stainlesssteel anode can with nickel plated surface.

Reference numeral 8 is a stainless steel mesh anode current collector,which is spot-welded to the inside of the anode can 7, and the anode 2is pressure-bonded to the stainless steel mesh anode current collector8. Reference numeral 9 is a polypropylene annular gasket, and thisbattery is filled with an organic electrolyte dissolving 1 mol/liter ofLiPF₆ into a mixed solvent of 1:1 ratio by volume of ethylene carbonateand methyl ethyl carbonate.

Please note, in Examples 1 to 4 and Comparative Examples 1 to 2 there isused the electrolyte while in the other Examples there is used anorganic electrolyte dissolving 0.6 mol/liter of LiCF₃ SO₃ into a mixedsolvent of 1:1 ratio by volume of ethylene carbonate and1,2-methoxyethane.

EXAMPLE 2

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were weighed to be a ratio of Li/Ni=1/1 (molar salt ratio), andpulverized and mixed by using a ball mill, and heated to synthesizelithium nickel oxide. The condition of synthesis was same as in Example1 except that the Li/Ni ratio (molar salt ratio) was changed to 1/1(molar salt ratio). That. is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 700°C. at heating rate of 50° C./hr or less, and baking at 700° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 2, and the line width (ΔHpp) between the peaks was 165mT.

The powder X-ray diffraction image of the synthesized lithium nickeloxide is schematically shown in FIG. 5. The intensity ratio of the mainpeak of other than lithium nickel oxide and the main peak of lithiumnickel oxide was 0.0099.

That is, the main peak of lithium nickel oxide was a peak appearing at2θ=18° to 19°, and its intensity was 84535 cps, and the main peak ofother than lithium nickel oxide was a peak appearing at 2θ=31.62°, andits intensity was 837 cps, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.0099 as mentioned above.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.90 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 1.

EXAMPLE 3

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were weighed to be a ratio of Li/Ni=1.3/1 (molar salt ratio), andpulverized and mixed by using a ball mill, and heated to synthesizelithium nickel oxide. The condition of synthesis was same as in Example1 except that the Li/Ni ratio (molar salt ratio) was changed to 1.3/1(molar salt ratio). That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 700°C. at heating rate of 50° C./hr or less, and baking at 700° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 2, and the line width (ΔHpp) between the peaks was 175mT.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 6. The intensity ratio of the main peakof other than lithium nickel oxide and the main peak of lithium nickeloxide was 0.016.

That is, the main peak of lithium nickel oxide was a peak appearing at2θ=18° to 19°, and its intensity was 99382 cps, and the main peak ofother than lithium nickel oxide was a peak appearing at 2θ=33.54°, andits intensity was 1635 cps, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.016 as mentioned above.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.94 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 1.

EXAMPLE 4

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were weighed to be a ratio of Li/Ni=1.5/1 (molar salt ratio), andpulverized and mixed by using a ball mill, and heated to synthesizelithium nickel oxide. The condition of synthesis was same as in Example1 except that the Li/Ni ratio (molar salt ratio) was changed to 1.5/1(molar salt ratio). That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 700°C. at heating rate of 50° C./hr or less, and baking at 700° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 2, and the line width (ΔHpp) between the peaks was 177mT.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 7. The intensity ratio of the main peakof other than lithium nickel oxide and the main peak of lithium nickeloxide was 0.029.

That is, the main peak of lithium nickel oxide was a peak appearing at2θ=18° to 19°, and its intensity was 96332 cps, and the main peak ofother than lithium nickel oxide was a peak appearing at 2θ=33.52°, andits intensity was 2795 cps, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.029 as mentioned above.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.94 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 1.

Comparative Example 1

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were weighed to be a ratio of Li/Ni=0.75/1 (molar salt ratio), andpulverized and mixed by using a ball mill, and heated to synthesizelithium nickel oxide. The condition of synthesis was same as in Example1 except that the Li/Ni ratio (molar salt ratio) was changed to 0.75/1(molar salt ratio). That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 700°C. at heating rate of 50° C./hr or less, and baking at 700° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured at temperature 77 K. by using X-band, but the electron spinresonance spectrum was not a primary differential absorption spectrum ofsinglet as in the foregoing embodiments, and a super-broad profile wasobtained as shown in FIG. 3, and its line width (ΔHpp) could not bedetected.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 8. The intensity ratio of the main peakof other than lithium nickel oxide and the main peak of lithium nickeloxide was 0.015.

That is, the main peak of lithium nickel oxide was a peak appearing at2θ=18° to 19°, and its intensity was 62656 cps, and the main peak ofother than lithium nickel oxide was a peak appearing at 2θ=19.72°, andits intensity was 934 cps, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.015 as mentioned above.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.72 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 1.

Comparative Example 2

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were weighed to be a ratio of Li/Ni=2.0/1 (molar salt ratio), andpulverized and mixed by using a ball mill, and heated to synthesizelithium nickel oxide. The condition of synthesis was same as in Example1 except that the Li/Ni ratio (molar salt ratio) was changed to 2.0/1(molar salt ratio). That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 700°C. at heating rate of 50° C./hr or less, and baking at 700° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 2, and the line width (ΔHpp) between the peaks was 178mT.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 9. The intensity ratio of the main peakof other than lithium nickel oxide and the main peak of lithium nickeloxide was as larger as 0.073, and it contained much of other thanlithium nickel oxide, or impurity.

That is, the main peak of lithium nickel oxide was a peak appearing at2θ=18° to 19°, and its intensity was 90601 cps, and the main peak ofother than lithium nickel oxide was a peak appearing at 2θ=33.52°, andits intensity was 6601 cps, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was as large as 0.073 as mentioned above.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.93 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 1.

The batteries of Examples 1 to 4 and batteries of Comparative Examples 1and 2 were charged and discharged at charging current of 0.393 mA anddischarging current of 0.393 mA (0.5 mA/cm² per unit area of cathode),between voltages 4.3 and 2.5 V.

In these batteries, since the lithium nickel oxide is used as thecathode active material, they were first charged, and Li was extractedfrom the lithium nickel oxide, and the lithium nickel oxide was used asLi_(1-x) NiO₂ (x>0).

Table 1 shows the material charging Li/Ni ratio in Examples 1 to 4 andComparative Examples 1 and 2, Li/Ni atomic ratio of synthesized lithiumnickel oxide, line width (ΔHpp) between peaks of electron spin resonancespectrum, intensity ratio of main peak of other than lithium nickeloxide and main peak of lithium nickel oxide, the average grain size ofthe first grain of synthesized lithium nickel oxide and charging anddischarging capacity.

In all of Examples 1 to 4 and Comparative Examples 1 and 2, the startingmaterials were lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide(III) (Ni₂ O₃), and Table 1 shows how 1) the line width (ΔHpp) ofelectron spin resonance spectrum, 2) the intensity ratio of main peak ofother than lithium nickel oxide and main peak of lithium nickel oxideand 3) the charging and discharging capacity, vary depending on thedifference of the material charging Li/Ni ratio (molar salt ratio).

                                      TABLE 1                                     __________________________________________________________________________                                   Comparative                                                 Example           Example                                                     1    2    3   4   1   2                                          __________________________________________________________________________    Material charging Li/Ni                                                                    1.1  1.0  1.3 1.5 0.75                                                                              2.0                                        ratio (molar ratio)                                                           Li/Ni ratio in lithium                                                                     0.93 0.90 0.94                                                                              0.94                                                                              0.72                                                                              0.93                                       nickel oxide (atomic ratio)                                                   ΔHpp (mT)                                                                            166  165  175 177 --  178                                        Intensity ratio of main                                                                    0.0098                                                                             0.0099                                                                             0.016                                                                             0.027                                                                             0.015                                                                             0.073                                      peak of other than                                                            lithium nickel oxide and                                                      main peak of lithium                                                          nickel oxide                                                                  average grain size (μm)                                                                 0.5  0.5  0.5 0.5 0.5 0.5                                        Charging and discharging                                                                   209  200  187 177 25  60                                         capacity (mAh/g)                                                              __________________________________________________________________________

As shown in Table 1, Examples 1 to 4 presented large charging anddischarging capacities of 209 mAh/g, 200 mAh/mg, 188 mAh/g and 177mAh/g, respectively. In these Examples 1 to 4, ΔHpp (line width betweenpeaks of electron spin resonance spectrum) was 166 mT, 165 mT, 175 mTand 177 mT, respectively, each of them was above 140 mT.

By contrast, Comparative Example 1 had a small charging and dischargingcapacity of 25 mAh/g. In this Comparative Example 1, the shape of theelectron spin resonance spectrum was different from that of theExamples, and ΔHpp could not be detected. That is, ΔHpp is to expressthe electron state of nickel in the lithium nickel oxide, and failure ofdetection of ΔHpp in Comparative Example 1 seems to suggest thatComparative Example 1 has a different electron state from Examples 1 to4 and is not suited to charging and discharging function.

Incidentally, that the electron state of lithium nickel oxide inComparative Example 1 is different from that of Examples 1 to 4 is notcontrary to the fact that the intensity is inverted between (003) peakand (104) peak, that is, the first peak at 2θ=18° to 19° and the secondpeak at 2θ=44° to 45° of Comparative Example 1 when the lithium nickeloxide is indexed as a hexagonal crystal in powder X-ray diffractionimage and that the crystal structure of Comparative Example 1 isestimated to be different from the crystal structure of Examples 1 to 4.

Although the electron state was not clear, it has been found for thefirst time by the inventors that ΔHpp is detected also at temperature 77K. in the structure of LiNiO₂ if the nickel is provided with valence of3 having at least unpaired electrons and the surrounding circumstance ofthe structure is suited to the charging and discharging function.

In Comparative Example 2, the charging and discharging capacity was alsosmall at 60 mAh/g. In this comparative Example 2, since the primarydifferential absorption spectrum of electron spin resonance is singletand ΔHpp is 178 mT, it seems to contain a same structure as in Examples1 to 4, but the impurity, that is, the peak of other than lithium nickeloxide is larger than in Examples 1 to 4, and the excess content oflithium becomes a compound other than lithium nickel oxide, which isconsidered to impede the charging and discharging reaction in thebattery to decrease the charging and discharging capacity in ComparativeExample 2.

Next Examples 5 to 7 and Comparative Examples 3 to 5 will make it clearhow the heat treatment temperature in synthesis of lithium nickel oxideeffect the Li/Ni ratio of the lithium nickel oxide and the charging anddischarging capacity of lithium secondary battery.

EXAMPLE 5

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated, andlithium nickel oxide was synthesized. This synthesis was conducted inthe following procedure. Lithium oxide and nickel oxide (III) wereweighed to be a ratio of Li/Ni=1.02/1 (molar salt ratio), and pulverizedand mixed by using an agate mortar. The mixture was preheated to 500° C.in oxygen (O₂) stream for 2 hours, and raised up to 700° C. at heatingrate of 50° C./hr or less, and baking at 700° C. was performed for 10hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 10, and the line width (ΔHpp) between the peaks was 152mT.

The powder X-ray diffraction image of the synthesized lithium nickeloxide is schematically shown in FIG. 12. According to the powder X-raydiffraction, the peak value of other than lithium nickel oxide, that is,the peak value of the impurity is less than detection limit andintensity ratio of the main peak of other than lithium nickel oxide andthe main peak of lithium nickel oxide was 0.03 or less.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.90 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as the cathode activematerial, a button type lithium secondary battery was fabricated in thesame manner as in Example 1.

Hereinafter, batteries including Example 5 use an organic electrolytedissolving 0.6 mol/liter of LiCF3SO₃ into a mixed solvent of 1:1 ratioby volume of ethylene carbonate and 1,2-methoxyethane.

EXAMPLE 6

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were heated at 700° C. to synthesize lithium nickel oxide. The conditionof synthesis was same as in Example 5 except that lithium oxide waschanged to lithium hydroxide hydrate. That is, as the heat treatment,the mixture was preheated to 500° C. in oxygen stream for 2 hours, andraised up to 700° C. at heating rate of 50° C./hr or less, and baking at700° C. was performed for 10 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 10, and the line width (ΔHpp) between the peaks was 164mT.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 13. According to the powder X-raydiffraction, the main peak of other than lithium nickel oxide was a peakappearing at 2θ=31.7°, but its peak was small, and the intensity ratioof the main peak of other than lithium nickel oxide and the main peak oflithium nickel oxide was 0.0071.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.93 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

EXAMPLE 7

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at780° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 5 except that the baking temperature was changedfrom 700° C. to 780° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 780°C. at heating rate of 50° C./hr or less, and baking at 780° C. wasperformed for 10 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singletas shown in FIG. 10 and the line width (ΔHpp) between the peaks was 146mT.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 14. According to the powder X-raydiffraction, the peak value of other than lithium nickel oxide is lessthan detection limit, and intensity ratio of the main peak of other thanlithium nickel oxide and the main peak of lithium nickel oxide was 0.03or less.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.93 and the average grain size of the primary particles was 1 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

Comparative Example 3

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at900° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 5 except that the baking temperature was changedfrom 700° C. to 900° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 900°C. at heating rate of 50° C./hr or less, and baking at 900° C. wasperformed for 10 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was notsinglet as Examples, and a super-broad profile was obtained as shown inFIG. 11, and its line width (ΔHpp) could not be detected.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 15. According to the powder X-raydiffraction, the main peak of other than lithium nickel oxide was a peakappearing at 2θ=33.6°, and the intensity ratio of the main peak of otherthan lithium nickel oxide and the main peak of lithium nickel oxide was0.014.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.82 and the average grain size of the primary particles was 10 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

Comparative Example 4

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at1100° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 5 except that the baking temperature was changedfrom 700° C. to 1100° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to1100° C. at heating rate of 50° C./hr or less, and baking at 1100° C.was performed for 10 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was notsinglet as Examples, ad a super-broad profile was obtained, and its linewidth (ΔHpp) could not be detected.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 16. Lithium nickel oxide in ComparativeExample 4 had different crystal form, and the main peak of other thanlithium nickel oxide was not found.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.41 and the average grain size of the primary particles was 50 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

Comparative Example 5

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at500° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 5 except that the baking temperature was changedfrom 700° C. to 500° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and baking at 500° C.was performed for 10 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the spectrum ofelectron spin resonance, shown in FIG. 10, was not a singlet primarydifferential absorption spectrum as in Examples, and broad and weak,then, the line width (ΔHpp) was impossible to be detected.

The powder X-ray diffraction image of the obtained lithium nickel oxideis schematically shown in FIG. 17. According to the powder X-raydiffraction image, the main peak of other than lithium nickel oxide wasa peak appearing at 2θ=31.43°, and the intensity ratio of the main peakof other than lithium nickel oxide and the main peak of lithium nickeloxide was 0.056 and a lot of impurities were found.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.43 and the average grain size of the primary particles was 0.45μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

The batteries of Examples 5 to 7 and batteries of Comparative Examples 3to 5 were charged and discharged at charging current of 0.393 mA anddischarging current of 0.393 mA (0.5 mA/cm² per unit area of cathode),between voltages 4.3 and 2.5 V. In these batteries, sine the lithiumnickel oxide was used as cathode active material, they were firstcharged, and Li was extracted from the lithium nickel oxide, and thelithium nickel oxide was used as Li_(1-x) NiO₂ (x>0).

Table 2 shows the baking temperature at synthesizing lithium nickeloxide in Examples 5 to 7 and Comparative Examples 3 to 5, Li/Ni atomicratio of synthesized lithium nickel oxide, the line width (ΔHpp) betweenpeaks of the primary differential absorption spectrum of electron spinresonance, the intensity ratio of the main peak of other than lithiumnickel oxide and the main peak of lithium nickel oxide, the averagegrain size of the primary grain of synthesized lithium nickel oxide andcharging and discharging capacity.

In all of Examples and Comparative Examples, the starting materials ofExamples 5 and 7 and Comparative Examples 3 to 5 were lithium oxide (Li₂O) and nickel oxide (III) (Ni₂ O₃), and Table 2 shows the line width(ΔHpp) of the electron spin resonance spectrum, the average grain sizeof the primary particles and the change of the charging and dischargingcapacity depending on the difference of the baking temperature.

                                      TABLE 2                                     __________________________________________________________________________                   Example              Comparative Example                                      5       6    7       3   4          5                          __________________________________________________________________________    Baking temperature (°C.)                                                              700     700  780     900 1100       500                        Li/Ni ratio in lithium                                                                       0.93    0.93 0.93    0.82                                                                              0.41       0.43                       nickel oxide (atomic ratio)                                                   ΔHpp (mT)                                                                              152     164  146     --  --         --                         Intensity ratio of main peak                                                                 less than                                                                             0.0071                                                                             less than                                                                             0.014                                                                             different crystal                                                                        0.056                      of other than lithium nickel                                                                 detection limit                                                                            detection limit                                                                           and impossible to                     oxide and main peak of lithium          detect                                nickel oxide                                                                  Average grain size (μm)                                                                   0.5     0.5  1       10  50         0.45                       Charging and discharging                                                                     189     221  153     69  5          37                         capacity (mAh/g)                                                              __________________________________________________________________________

As shown in Table 2, Examples 5 to 7 presented large charging anddischarging capacities of 189 mAh/g, 221 mAh/mg and 153 mAh/g,respectively. In these Examples 5 to 7, ΔHpp was 152 mT, 164 mT, 146 mTand 140 mT, respectively, each of them was 140 mT or more.

By contrast, Comparative Examples 3 to 5 presented small charging anddischarging capacity of 69 mAh/g, 5 mAh/g and 37 mAh/g, respectively. Inthese Comparative Examples 3 to 5, the shape of the electron spinresonance spectrum was different from that of the embodiments, and ΔHppcould not be detected.

That is, ΔHpp is to express the electron state of nickel in the lithiumnickel oxide, and the failures of detection of ΔHpp in ComparativeExamples 3 and 4 seem to suggest that Comparative Examples 3 and 4 havea different electron state from Examples 5 to 7 and is not suitable tocharging and discharging.

The electron state on lithium nickel oxides in Comparative Examples 3and 4 is different from those in Examples 5 to 7, and the crystalstructure of lithium nickel oxide in Comparative Examples 3 and 4 isthought to be different from those in Examples 5 to 7, and these doesnot conflict with each other.

Although the electron state was not clear, at least it was discoveredfor the first time in the present invention that ΔHpp is detected alsoat temperature 77 K. in the structure of LiNiO₂ suited to charging anddischarging in the surrounding circumstance, in the state of nickel withvalence of 3 having at least the unpaired electrons.

The lithium nickel oxide in Example 5 is calcined at 500° C., and thesignal of the electron spin resonance is weak, 1/4 as that of Example 5,so, we can think that the lithium nickel oxide does not fully react, sothe LiNiO₂ structure suitable for charging and discharging present onlypartially. We can get the same conclusion from the result of the powderX-ray diffraction analysis.

From these results, we can get a clear conclusion that a lithiumsecondary battery can be prepared using lithium nickel oxide whoseelectron state give the ΔHpp value more than 140 mT.

The following explanation is about the effect on the charging anddischarging capacity of the battery depending on the Li/Ni ratio oflithium nickel oxide and the average grain size of the primaryparticles.

EXAMPLE 8

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated tosynthesize lithium nickel oxide. This synthesis was conducted in thefollowing procedure.

Lithium oxide and nickel oxide were weighed to be a ratio of Li/Ni=1/1(molar salt ratio), and pulverized and mixed by using an agate mortar.The mixture was preheated to 500° C. in oxygen stream for 2 hours, andraised up to 700° C. at heating rate of 50° C./hr or less, and baking at700° C. was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,and the line width (ΔHpp) between the peaks was 150 mT.

According to the powder X-ray diffraction of synthesized lithium nickeloxide, the peak other than lithium nickel oxide, that is, the peak ofimpurities was less than the detection limit, moreover, the intensityratio of the main peak other than lithium nickel oxide and the main peakof lithium nickel oxide obtained from this powder X-ray diffractionimage was 0.03 or less.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.90 and the average grain size of the primary particles was 0.5 μm.

By using lithium nickel oxide prepared by heat treatment as the cathodeactive material, a button type lithium secondary battery was fabricatedas in the same manner in Example 5.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 5.

EXAMPLE 9

Lithium hydroxide hydrate (LiOH.H₂ O) and nickel oxide (III) (Ni₂ O₃)were heated at 700° C. to synthesize lithium nickel oxide. The conditionof synthesis was same as in Example 8 except that lithium oxide waschanged to lithium hydroxide hydrate. That is, as the heat treatment,the mixture was preheated to 500° C. in oxygen stream for 2 hours, andraised up to 700° C. at heating rate of 50° C./hr or less, and baking at700° C. was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,and the line width (ΔHpp) between the peaks was 165 mT.

According to the powder X-ray diffraction of the obtained lithium nickeloxide, the main peak of other than lithium nickel oxide was a peakappearing at 2θ=21.36°, but its peak was small, and the intensity ratioof the main peak of other than lithium nickel oxide and the main peak oflithium nickel oxide was 0.0090, which is below 0.03.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.90 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 8.

Comparative Example 6

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at800° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 8 except that the baking temperature was changedfrom 700° C. to 800° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 800°C. at heating rate of 50° C./hr or less, and baking at 800° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,but the line width (ΔHpp) was small as 135 mT.

According to the powder X-ray diffraction of the obtained lithium nickeloxide, the peak other than lithium nickel oxide was small and less thanthe detection limit.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.94 and the average grain size of the primary particles was 3 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 8.

Comparative Example 7

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at900° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 8 except that the baking temperature was changedfrom 700° C. to 900° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to 900°C. at heating rate of 50° C./hr or less, and baking at 900° C. wasperformed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, but the electron spinresonance spectrum was not a primary differential absorption spectrum ofsinglet as in the foregoing embodiments, a super-broad profile wasobtained ,and its line width (Δpp) could not be detected.

According to the powder X-ray diffraction of the obtained lithium nickeloxide, the main peak of other than lithium nickel oxide was a peakappearing at 2θ=33.66°, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.0084.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.82 and the average grain size of the primary particles was 10 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 8.

Comparative ExampLe 8

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at1100° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 8 except that the baking temperature was changedfrom 700° C. to 1100° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and raised up to1100° C. at heating rate of 50° C./hr or less, and baking at 1100° C.was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, but the electron spinresonance spectrum was not a primary differential absorption spectrum ofsinglet as in the foregoing embodiments, a super-broad profile wasobtained, and its line width (ΔHpp) could not be detected.

According to the powder X-ray diffraction of the synthesized lithiumnickel oxide, lithium nickel oxide in Comparative Example 8 haddifferent crystal construction and the main peak of other than lithiumnickel oxide was not found.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.41 and the average grain size of the primary particles was 50 μm.

Using thus synthesized lithium nickel oxide as the cathode activematerial, a button type lithium secondary battery was fabricated in thesame manner as in Example 8.

Comparative Example 9

Lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) were heated at500° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 8 except that the baking temperature was changedfrom 700° C. to 500° C. That is, as the heat treatment, the mixture waspreheated to 500° C. in oxygen stream for 2 hours, and baking at 500° C.was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was broadand a weak signal, then, its line width (ΔHpp) could not be detected.

According to the powder X-ray diffraction of the synthesized lithiumnickel oxide, the main peak of other than lithium nickel oxide was apeak appearing at 2θ=31.48°, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.055 and a lot of impurities were found.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.45 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as the cathode activematerial, a button type lithium secondary battery was fabricated in thesame manner as in Example 8.

Comparative Example 10

Lithium carbonate (Li₂ CO₃) and nickel carbonate (NiCO₃) were heated at700° C. to synthesize lithium nickel oxide. The condition of synthesiswas same as in Example 8 except that lithium oxide and nickel oxide(III) were changed to lithium carbonate and nickel carbonate,respectively. That is, as the heat treatment, the mixture was preheatedto 500° C. in oxygen stream for 2 hours, and raised up to 700° C. atheating rate of 50° C./hr or less, and baking at 700° C. was performedfor 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,but the line width (ΔHpp) was small as 117 mT.

According to the powder X-ray diffraction of the synthesized lithiumnickel oxide, the main peak of other than lithium nickel oxide was apeak appearing at 2θ=31.78°, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.0085.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.86 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as the cathode activematerial, a button type lithium secondary battery was fabricated in thesame manner as in Example 8.

Comparative Example 11

Lithium carbonate (Li₂ CO₃) and nickel nitrate haxahydrate [Ni(NO₃)₂.6H₂O] were heated at 700° C. to synthesize lithium nickel oxide. Thecondition of synthesis was same as in Example 8 except that lithiumoxide and nickel oxide were changed to lithium carbonate and nickelnitrate hexahydate, respectively. That is, as the heat treatment, themixture was preheated to 500° C. in oxygen stream for 2 hours, andraised up to 700° C. at heating rate of 50° C./hr or less, and baking at700° C. was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,but the line width (ΔHpp) was small as 106 mT.

According to the powder X-ray diffraction of the synthesized lithiumnickel oxide, the main peak of other than lithium nickel oxide was apeak appearing at 2θ=33.54° and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.0060.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.88 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 8.

Comparative Example 12

Lithium nitrate (LiNO₃) and nickel carbonate (NiCO₃) were heated at 700°C. to synthesize lithium nickel oxide. The condition of synthesis wassame as in Example 8 except that lithium oxide and nickel oxide (III)were changed to lithium nitrate and nickel carbonate, respectively. Thatis, as the heat treatment, the mixture was preheated to 500° C. inoxygen stream for 2 hours, and raised up to 700° C. at heating rate of50° C./hr or less, and baking at 700° C. was performed for 20 hours.

The electron spin resonance of the synthesized lithium nickel oxide wasmeasured in the same condition as in Example 1, and the primarydifferential absorption spectrum of electron spin resonance was singlet,but the line width (ΔHpp) was small as 104 mT.

According to the powder X-ray diffraction of the synthesized lithiumnickel oxide, the main peak of other than lithium nickel oxide was apeak appearing at 2θ=21.32°, and the intensity ratio of the main peak ofother than lithium nickel oxide and the main peak of lithium nickeloxide was 0.0072.

The Li/Ni ratio (atomic ratio) in the synthesized lithium nickel oxidewas 0.88 and the average grain size of the primary particles was 0.5 μm.

Using thus synthesized lithium nickel oxide as cathode active material,a button type lithium secondary battery was fabricated in the samemanner as in Example 8.

The batteries of Examples 8 and 9 and batteries of Comparative Examples6 to 12 were charged and discharge at charging current of 0.393 mA anddischarging current of 1.57 mA (2 mA/cm² per unit area of cathode),between voltages 4.3 and 2.5 V.

In these batteries, sine the lithium nickel oxide is used as cathodeactive material, they were first charged, and Li was extracted from thelithium nickel oxide, and the lithium nickel oxide was used as Li_(1-x)NiO₂ (x>0).

Table 3 shows relations between 1) the baking temperature atsynthesizing lithium nickel oxide in Examples 8 and 9 and ComparativeExamples 6 to 9, 2) the Li/Ni ratio of synthesized lithium nickel oxide,3) the line width (ΔHpp) between peaks of the primary differentialabsorption spectrum of electron spin resonance, 4) the intensity ratioof main peak of other than lithium nickel oxide and main peak of lithiumnickel oxide, 5) the average grain size of the primary grain ofsynthesized lithium nickel oxide and 6) the charging and dischargingcapacity. In these Examples and Comparative Examples, the startingmaterials were lithium oxide (Li₂ O) and nickel oxide (III) (Ni₂ O₃) ineach of Example 8 and Comparative Examples 6 to 9, and Table 3 shows howthe Li/Ni atomic ratio of synthesized lithium nickel oxide, the averagegrain size and the charging and discharging capacity vary depending onthe difference of the baking temperature.

Furthermore, Table 4 shows relations between 1) the starting materialsof Examples 8 and 9 and Comparative Examples 10 to 12, 2) the Li/Niatomic ratio of synthesized lithium nickel oxide, 3) the line width(ΔHpp) between peaks of the primary differential absorption spectrum ofelectron spin resonance and 4) the charging and discharging capacity. Inthese Examples 8 and 9 and Comparative Examples 10 to 12, the startingmaterials of were different but the baking temperature were all 700° C.and the average grain size of products were all 0.5 μm. Table 4 showshow the Li/Ni atomic ratio of the synthesized lithium nickel oxide andthe charging and discharging capacity vary depending on the differenceof the starting materials.

                                      TABLE 3                                     __________________________________________________________________________                   Example      Comparative Example                                              8       9    6       7    8          9                         __________________________________________________________________________    Baking temperature (°C.)                                                              700     700  800     900  1100       500                       Li/Ni ratio in lithium                                                                       0.90    0.90 0.94    0.82 0.41       0.45                      nickel oxide (atomic ratio)                                                   ΔHpp (mT)                                                                              150     165  135     --   --         --                        Intensity ratio of main peak                                                                 less than                                                                             0.0090                                                                             less than                                                                             0.0084                                                                             different crystal                                                                        0.055                     of other than lithium nickel                                                                 detection limit                                                                            detection limit                                                                            and impossible to                    oxide and main peak of lithium           detect                               nickel oxide                                                                  Average grain size (μm)                                                                   0.5     0.5  3       10   50         0.5                       Charging and discharging                                                                     160     200  109     67   0          33                        capacity (mAh/g)                                                              __________________________________________________________________________

As shown in Table 3, Examples 8 and 9 presented the large charging anddischarging capacities of 160 mAh/g and 200 mAh/m, respectively bycontrast to Comparative Examples 6 to 8. The result shows that thebaking temperature is preferred to be low of 700° C. and the smallergrain size has good characteristics.

By contrast, Comparative Example 9 presented the small charging anddischarging capacity of 33 mAh/g, which causes from that a bakingtemperature as low as 500° C. can not make the reaction proceedsufficiently, so that sufficient lithium nickel oxide can not beobtained. In Comparative Example 6, the Li/Ni ratio (atomic ratio) is0.94, close to 1, but the grain size of lithium nickel oxide is small tomake the charging and discharging small. Further, in Comparative Example6, the line width (ΔHpp) between peaks of the primary differentialabsorption spectrum of electron spin resonance is below 140 mT as shownin Table 3. It is believed that such small ΔHpp makes the charging anddischarging capacity small.

                                      TABLE 4                                     __________________________________________________________________________                     Li/Ni ratio                                                                          ΔHpp                                                                        Charging and discharging                                 Raw material                                                                            (atomic ratio)                                                                       (mT)                                                                              capacity (mAh/g)                                  __________________________________________________________________________    Example 8                                                                            Li.sub.2 O + Ni.sub.2 O.sub.3                                                           0.90   150 160                                               Example 9                                                                            LiOH.H.sub.2 O + Ni.sub.2 O.sub.3                                                       0.90   165 200                                               Comparative                                                                          Li.sub.2 CO.sub.3 + NiCO.sub.3                                                          0.86   117 138                                               Example 10                                                                    Comparative                                                                          Li.sub.2 CO.sub.3 + Ni(NO.sub.3).sub.2                                                  0.88   106 135                                               Example 11                                                                    Comparative                                                                          LiNO.sub.3 + NiCO.sub.3                                                                 0.88   104 128                                               Example 12                                                                    __________________________________________________________________________

As shown in Table 4, both Examples 8 and 9 presented Li/Ni atomic ratioof lithium nickel oxide of 0.90 and large charging and dischargingcapacity by contrast to Comparative Examples 10 to 12.

That is, Examples 8 and 9 using nickel oxide (III) (Ni₂ O₃) containingnickel with valence of 3 as starting material, presented the chargingand discharging capacity as large as 160 mAh/g and 200 mAh/g,respectively, compared with Comparative Examples 10 to 12 which usedanother starting material.

In the above Examples, the baking was carried out in the oxygen stream,but it can be carried out under the oxygen pressure. Furthermore,lithium nickel oxide was synthesized by lithium oxide(Li₂ O) and nickeloxide (III) (Ni₂ O₃) as the starting material while changing the oxygendensity. Higher the oxygen density becomes, closer to 1 the Li/Ni atomicratio is.

Furthermore, the Li/Ni ratio (atomic ratio) of lithium nickel oxide was0.9 or more in the present invention, but all the Li/Ni ratio shown inExamples are not beyond "1". As a result of the present invention,however, it is possible to use it as cathode active materials, what theLi/Ni ratio exceeded 1, for example, Li_(1+x) Ni_(1-x) O₂ (x>0, lithiumnickel oxide of Li excess), Li₂ NiO₂ and Li₂ NiO_(3-a), although thecharacteristics such as voltage and capacity are different.

INDUSTRIAL APPLICABILITY

As mentioned herein, according to the present invention, there isprovided a lithium secondary battery with a larger charging anddischarging capacity by using, as a cathode active material, a lithiumnickel oxide of which primary differential absorption spectrum ofelectron spin resonance measured at temperature 77 K. by using X band isa singlet, and the intensity ratio of main peak of other than lithiumnickel oxide and main peak of lithium nickel oxide in powder X-raydiffraction image (CuKα ray) is 0.03 or less.

What is claimed is:
 1. A lithium secondary battery, which comprises:acathode comprising a lithium nickel oxide as an active material, ananode comprising lithium or a compound containing lithium and an organicelectrolyte, wherein the cathode active material is a lithium nickeloxide having a primary differential absorption spectrum of electron spinresonance measured at a temperature of 77 K. by using X band that is asinglet, and an intensity ratio of a main peak other than lithium nickeloxide and a main peak of lithium nickel oxide in a powder X-raydiffraction image (CuKα ray) that is 0.03 or less.
 2. The lithiumsecondary battery containing organic electrolyte according to claim 1,wherein the lithium nickel oxide has an electronic structure whichindicates the line width (ΔHpp) between the peaks of the primarydifferential absorption spectrum of the electron spin resonance measuredat a temperature of 77 K. by using X band is 140 mT or more.
 3. Alithium secondary battery containing organic electrolyte according toclaims 1 or 2, wherein Li/Ni ratio (atomic ratio) of the said lithiumnickel oxide is 0.9 or more and the average grain size of the primaryparticles is 1 μm or less.
 4. A cathode active material for a lithiumsecondary battery containing an organic electrolyte, mainly composed ofa lithium nickel oxide having a primary differential absorption spectrumof electron spin resonance measured at a temperature of 77 K. by using Xband that is a singlet, and an intensity ratio of a main peak other thanlithium nickel oxide and a main peak of lithium nickel oxide in a powderX-ray diffraction image (CuKα ray) that is 0.03 or less.
 5. A cathodeactive material for the lithium secondary battery containing an organicelectrolyte according to claim 4, wherein the lithium nickel oxide hasan electronic structure which indicates the line width (ΔHpp) betweenthe peaks of the primary differential absorption spectrum of theelectron spin resonance measured at a temperature of 77 K. by using Xband is 140 mT or more.
 6. A cathode active material for the lithiumsecondary battery containing an organic electrolyte according to claim 4or 5, wherein said lithium nickel oxide possesses a Li/Ni ratio (atomicratio) of 0.9 or more, and wherein an average grain size of the primaryparticles thereof is 1 μm or less.
 7. A method of synthesizing thelithium nickel oxide of the cathode in the lithium secondary batteryaccording to claim 1, 2 or 3, which comprises the steps of:mixing anickel oxide containing nickel with a valence of 3 or more, or a nickelsalt producing nickel with a valence of 3 or more by heating, and alithium salt, at a ratio of Li/Ni (molar salt ratio) of 1.0 to 1.5, andheating the mixture at a temperature of 680° to 780° C.
 8. A method ofsynthesizing the lithium nickel oxide of the cathode in the lithiumsecondary battery according to claim 7, wherein the nickel oxidecontaining nickel with valence of 3 or more is Ni₂ O₃.
 9. A method ofsynthesizing the lithium nickel oxide of the cathode in the lithiumsecondary battery according to claim 8, wherein the heating takes placein an atmosphere that is an oxygen stream or under an oxygen pressure.10. A method of synthesizing the lithium nickel oxide according to claim3 used for a lithium secondary battery containing an organic electrolytewhich comprises steps of:mixing nickel oxide containing nickel withvalence of 3 or more or nickel salt producing nickel with valence of 3or more by heating, and lithium salt, at a ratio of Li/Ni (molar saltratio)=1.0 to 1.5, and heating the mixture at a temperature of 680° to780° C.